Most democratic countries attempt to regulate electoral finance, imposing restriction on who can donate to parties and candidates, how much they can contribute, how the money can be used and how donations must be disclosed. Some even offer partial or total public funding to reduce the dependence of parties on donations. However, there is a wide range of variation in the form and extent of such regulations. Theories of electoral regulation fall into two camps: those that emphasize the public benefit of such regulations and those that emphasize the anti-competitive incentives of parties in office in enacting such rules. Thus far, such theories have only been tested in the context of particular electoral reforms in small sets of countries. This paper offers the first systematic cross-national test of arguments concerning the structural and institutional determinants of variation in electoral finance regulation. It employs an index of national regulation which incorporates 29 different measures of electoral finance regulation and includes data on the legal sources of donations, their tax status, rules governing media access, direct public funding, spending limits, income limits, disclosure, and enforcement.